all: rename Tlv namespace to tlv for consistency

This commit renames the Tlv namespace defined in
tlv.hpp to tlv to be more consistent with tlv::security
and tlv::nfd. A Tlv namespace alias is provided for
backwards compatibility.

Change-Id: I21278d6a077afe7776802c3296997d4c1c44c6c6
diff --git a/src/security/sec-public-info-sqlite3.cpp b/src/security/sec-public-info-sqlite3.cpp
index 774dfb3..0c70d02 100644
--- a/src/security/sec-public-info-sqlite3.cpp
+++ b/src/security/sec-public-info-sqlite3.cpp
@@ -485,7 +485,7 @@
       std::string signerName = certificate.getSignature().getKeyLocator().getName().toUri();
       sqlite3_bind_text(statement, 2, signerName, SQLITE_TRANSIENT);
     }
-  catch (Tlv::Error& e)
+  catch (tlv::Error& e)
     {
       return;
     }